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its not really the balance shaft that is the issue. Its the whole design of the 3.8 in 1988 that makes it the winner of choice in my opinion. Im no certified or schooled mechanic and i have a lot to learn but this cross road is where i have come to be the most rational approach.

The 4.2L is a 3.8 block with a stroker kit and a bunch of other wing ding bolt ons.

The 4.2 crank is a solid tempered steel hunk of metal (this is a good thing since it can be turned more than a cast iron crank that has only tempered journals. If you turn a cast iron crank to much, you get to the soft metal. This is unlike the shorter stroke of the cast iron 3.8 crank and makes the cast iron less desirable compared to the 4.2. Im pretty sure the 88 3.8 crank is also steel and not cast iron.

My 4.2 crank out in the garage has been drilled along the oil slingers for balance.,,just fyi

Its not the balance shaft that ist he issue, its just locating like 3.8's with the exact short block configuration so you an put in the 4.2 kit.

There is a long ass thread of mine in engine swapping on this where i ultimatly ended up at a roadblock due to a bad engine.

If you just put the 4.2 stuff in an 87 and down engine,, im not really sure how it would run due to the lack of it being balanced the same. I am pretty sure the 3.8 harmonic will not slip on the nipple of the 4,2 crank, so,,, since the 4.2 never came with a harmonic, it stands to reason you would wanna stick with a compareable design.

Maybe tomorrow ill clear this up ,, ill see if my 87 3.8 harmonic fits the 4.2 crank. If it does fit,, then maybe thats what a guy named Rick on therangerstation.com means when he says "the 4.2L short block internals are a direct swap in the 3.8". If the harmonic fits, then is a tempting upgrade for all 3.8's. I just avoided using my block cause its externally balanced.

I also feel its a benefit to mention that the 4.2 connecting rods are forged "H" beam in design and much more durable than the earlier 3.8 rods. I can tell they are much more duable than the earlier 3.8's because the rod caps are "broken off" instead of cut. Makes for a real real fool proof system when reassembly comes around because no two rod caps are alike.

The 4.2 is a floating piston design as well, just fyi.

Now,, hows this for an idea,, Destroke **any** 3.8 and just use the rods and pistons from the 4.2, keep your crank. That would be a huge rpm range gain due to less Rod Angle / wear and tear / vibration not to mention a longer lasting setup in the HP arena. ANy thoughts on this last comment?????????????

If you just put the 4.2 stuff in an 87 and down engine,, im not really sure how it would run due to the lack of it being balanced the same. I am pretty sure the 3.8 harmonic will not slip on the nipple of the 4,2 crank, so,,, since the 4.2 never came with a harmonic, it stands to reason you would wanna stick with a compareable design.

As long as you used the 4.2 front pulley (or balancer or whatever it is) and flywheel you should be able to use the 4.2 guts in the 87-and-older blocks. The block itself has nothing to do with balance - it's all in the crank, flywheel and balancer. There would be no need to use the 3.8 balancer - indeed, if the two engines are balanced differently it would actually kill the engine.

I also feel its a benefit to mention that the 4.2 connecting rods are forged "H" beam in design and much more durable than the earlier 3.8 rods. I can tell they are much more durable than the earlier 3.8's because the rod caps are "broken off" instead of cut. Makes for a real real fool proof system when reassembly comes around because no two rod caps are alike.

The 4.2 is a floating piston design as well, just fyi.

Now,, hows this for an idea,, Destroke **any** 3.8 and just use the rods and pistons from the 4.2, keep your crank. That would be a huge rpm range gain due to less Rod Angle / wear and tear / vibration not to mention a longer lasting setup in the HP arena. ANy thoughts on this last comment?????????????

That might work but would result in a very low compression ratio. The 3.8 crank wouldn't allow the pistons to come all the way up in their bores. The 4.2 rods are slightly longer than the 3.8 (about 0.20") but the compression height of the pistons (distance from top of piston to pin) is about .35" shorter, meaning your piston would now come to TDC about .15" lower in the bore.

Add to that:
Truck 4.2 longblock w/ 97computer for manual transmission. That way I can mount it to an AOD and use a return style fuel system.
A bigger issue for me will be wiring up the dash and A/C differences. Are ANY of the senders from an EEC-V system compatible with a dash from an EEC-IV system?